Description

The Drake Equation was developed by Frank
Drake in 1961 as a way to focus on the factors which determine how
many intelligent, communicating civilizations there are in our galaxy.
The Drake Equation is:

N = N* fp ne
fl fi fc
fL

The equation can really be looked at as a number of questions:

N* represents the number of stars in the
Milky Way Galaxy

Question: How many stars are in the Milky Way Galaxy?

Answer: Current estimates are 100 billion.

fp is the fraction of stars that have planets
around them

Question: What percentage of stars have planetary systems?

Answer: Current estimates range from 20% to 50%.

ne is the number of planets per star that
are capable of sustaining life

Question: For each star that does have a planetary system, how
many planets are capable of sustaining life?

Answer: Current estimates range from 1 to 5.

fl is the fraction of planets in ne
where life evolves

Question: On what percentage of the planets that are capable
of sustaining life does life actually evolve?

Answer: Current estimates range from 100% (where life can evolve
it will) down to close to 0%.

fi is the fraction of fl
where intelligent life evolves

Question: On the planets where life does evolve, what percentage
evolves intelligent life?

Answer: Estimates range from 100% (intelligence is such a survival
advantage that it will certainly evolve) down to near 0%.

fc is the fraction of fi
that communicate

Question: What percentage of intelligent races have the means
and the desire to communicate?

Answer: 10% to 20%

fL is fraction of the planet's life during
which the communicating civilizations live

Question: For each civilization that does communicate, for what
fraction of the planet's life does the civilization survive?

Answer: This is the toughest of the questions. If we take Earth
as an example, the expected lifetime of our Sun and the Earth is roughly
10 billion years. So far we've been communicating with radio waves for
less than 100 years. How long will our civilization survive? Will we destroy
ourselves in a few years like some predict or will we overcome our problems
and survive for millennia? If we were destroyed tomorrow the answer to
this question would be 1/100,000,000th. If we survive for 10,000 years
the answer will be 1/1,000,000th.

When all of these variables are multiplied together when come up with:

N, the number of communicating civilizations
in the galaxy.

The real value of the Drake Equation is not in the answer
itself, but the questions that are prompted when attempting to come up
with an answer. Obviously there is a tremendous amount of guess
work involved when filling in the variables. As we learn more from astronomy,
biology, and other sciences, we'll be able to better estimate the answers
to the above questions. Many of these questions will be addressed in depth
in future issues of Enigma.

Try the Drake Equation Yourself

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Try your hand at the Drake Equation. For each variable choose what you
think is the best answer from the combo box. After you've chosen all your
answers press the calculate button and see how many communicating civilizations
you think there are in the galaxy.

N* = the number of stars in the Milky Way
galaxy:

fp = fraction of stars with planets around
them:

ne = number of planets per star ecologically
able to sustain life:

fl = fraction of those planets where life
actually evolves:

fi = the fraction of fl
that evolves intelligent life:

fc = the fraction of fi
that communicates:

fL = the fraction of the planet's life during
which the communicating civilizations survives: